Electrical motors are the main means by which electrical energy is changed into mechanical energy. There are several different types of motors in industrial use today, these can general be grouped into two main types, brush-type and brushless motors. DC motors with a magnetic field from permanent magnets typically provides higher torque in comparison with conventional asynchronous AC motors. This is achieved because the magnetizing flux is typically higher. The two magnetic fluxes (rotor and stator) are maintained at 90 degrees from each other to generate the highest torque. In a conventional DC motor with brushes the stator generates the magnetization fluxes: this can be achieved by a permanent magnet. The rotor is the main winding and the mechanical commutation insures proper feeding in the windings by the synchronized rotation of the set of conductive segments in contact with the static power feeding brushes. Typically the copper segments are mounted near the rotor shaft and rotate with the shaft. The copper segments are then connected to the rotor winding. When the rotor moves the current distribution is then performed.
In order to avoid conductive paths being established between the brushes, the gaps between the segments are clean or filled with “varnish or mica insulation. However overtime these gaps can be coated or filled with a thin layer of graphite powder from the brushes which could generate short-circuit between different elements connected at different voltages. As the brushes are generally graphite depending on the application they may typically only operate for a few months before being fully eroded and need replacing.
In mechanical commutation the heat generation in the commutation system will use up a percentage of the motor power. In conventional motors the heat is evacuated by proper contact of the brushes to the chassis of the stator, while the collector is in contact with the shaft so that heat can be moved to the main rotor body and evacuated as the rest of the winding loss in the rotor. Heat can also be partially removed by air flow which is forced axially between the rotor and stator to cool these elements. The air flow also transports carbon and copper dust from the commutation system out of the motor and helps the system stay clean.
The elements of the collector are typically small rectangular segments. This shape is required due to the high number of segments installed on the periphery of the collector. The long axial dimension is beneficial to limit the current density under the brushes when the segment is leaving the brushes, at that moment the winding inductance tends to keep the current at high value while the contact surface is reducing.
In DC brushless motors the main windings are in the stator and the rotor is a rotating permanent magnet. In this type of application the control circuit feed power to the stator winding that the stator magnetic flux is at 90 degrees from the rotor flux. This is achieved due to sensors that continuously track the rotor position.
In another application DC power may be transmitted to the rotor of the machine, in this situation the rotary DC magnetizing flux of such machine is obtained from rotating winding feed with DC current. In this application two brushes are used and each brush is in continuous contact with one solid rotating ring.
Submerged motors are used in various pumping application. One is in the circulating pump of central heating systems for houses and buildings, another use is in the motors for electrical submersible pumps (ESP) used in the oil field. In both cases asynchronous motors are commonly used. With AC systems, particularly 3 phases AC motors, the use of several windings at proper angles generates a rotary magnetic field which interacts with induction flux of the rotor (the flux obtained by a permanent magnet, by field winding, or by self induced current appearing in the rotor (in the squirrel cage)). With the interaction, the rotor is set in rotation. With such a design there is no need for commutation making them suitable for submerged applications.
However the power per unit of volume is reduced compared to a DC motor. These motors require more expensive wiring and more complex systems for speed control.
Therefore it is an object of the invention to provide a new design for a commutation system that is suitable for submerged applications.